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Message-ID: <YE9mVUF0KOPNSfA9@kernel.org>
Date: Mon, 15 Mar 2021 15:51:17 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Kai Huang <kai.huang@...el.com>
Cc: Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
linux-sgx@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org, luto@...nel.org,
dave.hansen@...el.com, rick.p.edgecombe@...el.com,
haitao.huang@...el.com, pbonzini@...hat.com, bp@...en8.de,
tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH v2 07/25] x86/sgx: Initialize virtual EPC driver even
when SGX driver is disabled
On Mon, Mar 15, 2021 at 03:04:59PM +0200, Jarkko Sakkinen wrote:
> On Mon, Mar 15, 2021 at 04:13:17PM +1300, Kai Huang wrote:
> > On Sun, 14 Mar 2021 17:27:18 +0200 Jarkko Sakkinen wrote:
> > > On Sun, Mar 14, 2021 at 05:25:26PM +0200, Jarkko Sakkinen wrote:
> > > > On Sat, Mar 13, 2021 at 09:07:36PM +0200, Jarkko Sakkinen wrote:
> > > > > On Sat, Mar 13, 2021 at 09:05:36PM +0200, Jarkko Sakkinen wrote:
> > > > > > On Fri, Mar 12, 2021 at 01:44:58PM -0800, Sean Christopherson wrote:
> > > > > > > On Tue, Mar 09, 2021, Kai Huang wrote:
> > > > > > > > Modify sgx_init() to always try to initialize the virtual EPC driver,
> > > > > > > > even if the SGX driver is disabled. The SGX driver might be disabled
> > > > > > > > if SGX Launch Control is in locked mode, or not supported in the
> > > > > > > > hardware at all. This allows (non-Linux) guests that support non-LC
> > > > > > > > configurations to use SGX.
> > > > > > > >
> > > > > > > > Acked-by: Dave Hansen <dave.hansen@...el.com>
> > > > > > > > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > > > > > > > ---
> > > > > > > > arch/x86/kernel/cpu/sgx/main.c | 10 +++++++++-
> > > > > > > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > > > > > > >
> > > > > > > > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> > > > > > > > index 44fe91a5bfb3..8c922e68274d 100644
> > > > > > > > --- a/arch/x86/kernel/cpu/sgx/main.c
> > > > > > > > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > > > > > > > @@ -712,7 +712,15 @@ static int __init sgx_init(void)
> > > > > > > > goto err_page_cache;
> > > > > > > > }
> > > > > > > >
> > > > > > > > - ret = sgx_drv_init();
> > > > > > > > + /*
> > > > > > > > + * Always try to initialize the native *and* KVM drivers.
> > > > > > > > + * The KVM driver is less picky than the native one and
> > > > > > > > + * can function if the native one is not supported on the
> > > > > > > > + * current system or fails to initialize.
> > > > > > > > + *
> > > > > > > > + * Error out only if both fail to initialize.
> > > > > > > > + */
> > > > > > > > + ret = !!sgx_drv_init() & !!sgx_vepc_init();
> > > > > > >
> > > > > > > I love this code.
> > > > > > >
> > > > > > > Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> > > > > >
> > > > > > I'm still wondering why this code let's go through when sgx_drv_init()
> > > > > > succeeds and sgx_vepc_init() fails.
> > > > > >
> > > > > > The inline comment explains only the mirrored case (which does make
> > > > > > sense).
> > > > >
> > > > > I.e. if sgx_drv_init() succeeds, I'd expect that sgx_vepc_init() must
> > > > > succeed. Why expect legitly anything else?
> > > >
> > > > Apologies coming with these ideas at this point, but here is what this
> > > > led me.
> > > >
> > > > I think that the all this complexity comes from a bad code structure.
> > > >
> > > > So, what is essentially happening here:
> > > >
> > > > - We essentially want to make EPC always work.
> > > > - Driver optionally.
> > > >
> > > > So what this sums to is something like:
> > > >
> > > > ret = sgx_epc_init();
> > > > if (ret) {
> > > > pr_err("EPC initialization failed.\n");
> > > > return ret;
> > > > }
> > > >
> > > > ret = sgx_drv_init();
> > > > if (ret)
> > > > pr_info("Driver could not be initialized.\n");
> > > >
> > > > /* continue */
> > > >
> > > > I.e. I think there should be a single EPC init, which does both EPC
> > > > bootstrapping and vepc, and driver initialization comes after that.
> > >
> > > In other words, from SGX point of view, the thing that KVM needs is
> > > to cut out EPC and driver part into different islands. How this is now
> > > implemented in the current patch set is half-way there but not yet what
> > > it should be.
> >
> > Well conceptually, SGX virtualization and SGX driver are two independently
> > functionalities can be enabled separately, although they both requires some
> > come functionalities, such as /dev/sgx_provision, which we have moved to
> > sgx/main.c exactly for this purpose. THerefore, conceptually, it is bad to make
> > assumption that, if SGX virtualization initialization succeeded, SGX driver
> > must succeed -- we can potentially add more staff in SGX virtualization in the
> > future..
> >
> > If the name sgx_vepc_init() confuses you, I can rename it to sgx_virt_init().
>
> I don't understand what would be the bad thing here. Can you open that
> up please? I'm neither capable of predicting the future...
Right, so since vepc_init() does only just device file initialization the
current function structure is fine. I totally forgot that sgx_drv_init()
does not call EPC initialization when I wrote the above :-) We refactored
during the inital cycle the driver so many times that I sometimes fix up
thing, sorry about.
To meld this into code:
ret = sgx_vepc_init();
if (ret != -ENODEV) {
pr_err("vEPC initialization failed with %d.\n", ret);
return ret;
}
ret = sgx_drv_init();
if (ret != ENODEV)
pr_info("Driver initialization failed %d.\n", ret);
This would also give more accurate information how far the initialization
went.
/Jarkko
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